The need to be able to quantitatively characterize very fine structures, buried in the first nanometers of solid materials of the semiconductor type for example, has never stopped growing over the years. This is especially the case in the field of microelectronics. The increase in the speed of electronic circuits is determined by market needs. This increase in speed is accomplished, by reducing the size of these circuits and therefore of the structural elements that make up the transistors.
Thus, the minimum size of these transistors has decreased from 2 μm in 1980 to 180 nm today. The intended objective is to bring transistors having sizes of 130 nm and 100 nm into service in the coming years, and of 50 nm thereafter.
The production of such submicron transistors implies control over the steps of forming very fine structures, the thickness of which does not exceed, for example, 50 nm. In particular, two fabrication steps are very important:                ion implantation of charge carriers, which may be carried out over a thickness already not exceeding a few nanometers before activation;        the covering of the transistor with a gate dielectric material, in the form of a layer of material whose thickness is henceforth sometimes less than one nanometer. Thicknesses of this order represent quantities of atoms typically between 1013 and 1016 atoms per cm2.        
Faced with the production difficulties, semiconductor manufacturers are seeking industrial analytical devices that are capable of reliably characterizing the submicron structures produced. These devices must be sufficiently sensitive and accurate to be able to quantify and monitor, typically with a precision of within 1%, the composition and thickness characteristics of the structures fabricated. These devices must also have a resolution sufficient to allow an analytical check to be made in very small regions that are dedicated for these tests and located on the border of the electronic chips. The size of the test regions is typically of the order of 100 μm×100 μm. These devices must also establish diagnostics over times compatible with the constraints associated with the production environment. These times are, for example, of the order of a few minutes for inspecting a wafer.
Since the structures produced are becoming finer and finer, to be able to check them requires increasingly precise measurements to be carried out. As regards orders of magnitude of the measurements to be performed, the devices currently available on the market are inappropriate and of insufficient performance. This lack of performance impinges on several aspects, from the lack of precision in the quantitative results to purely and simply the lack of sensitivity.